1. Field of the Invention
The present invention relates to a MOS solid-state image pickup device provided with vertical overflow drains More particularly, the invention relates to an external shutter-equipped electronic still picture camera capable of increasing the dynamic range with respect to the brightness of a scene to be picked up.
2. Description of the Prior Art
Generally, each of the photodiodes arranged in a photo-detecting section of a solid-state image pickup device generates charges in an amount proportional to the intensity of light and there is a limitation with respect to the amount of charge which can be stored in the photodiode. Therefore, if the brightness of the scene to be picked up is high, the stored charges of the photodiode are saturated in a short period of time. In view of this fact, Japanese Laid-Open Patent Application No. 58-6682, Jan. 14, 1983, discloses an IT-CCD (interline transfer-charge coupled device) which provides a solid-state image pickup device with a characteristic designed to vary the storage capacity for charges generated from the photodiodes with time and thereby increase the dynamic range of the image pickup device for the brightness of the scene to be picked up.
In Japanese Laid-Open Patent Application No. 58-6682, the read-out gate units are controlled so that during the period of exposure to light, the potential of each read-out gate unit (which may also be called a transfer gate) for transferring the charges from the photodetector to each vertical transfer unit has at least two different levels, thereby allowing the charges from the photodetector to flow to the vertical transfer unit through the read-out gate unit. However, the charges transferred to the vertical transfer units must be delivered to the outside by a driving operation of applying pulses to the vertical transfer units and a horizontal transfer unit and corresponding to at least one field. Also, where the charges in the vertical transfer units are transferred in the opposite direction, means must be additionally provided to deliver the transferred charges to the outside.